Typical lowest order Feynman graphs relevant for the 3-body twist-3 contributions are shown
in Fig. REF  b-c. The 16 Feynman graphs (b) and (c)
make up the 3-body contribution. Graphs of type (d) for which the constituent
gluon of the pion couples to one of its quark constituents, are soft contributions and are to
be considered as parts of the 2-body twist-3 meson DA. In light-cone gauge
the gluon field, \(A_\mu (x)\) , appearing in perturbation theory, is related to the gluon field
strength tensor \(G_{\mu \nu }\)  which defines the 3-body DA, \(\phi _{3\pi }\) , [1]}
by (\(n\)  being a light-like vector)
\(A^r_\rho (z) \,=\,\lim _{\epsilon \rightarrow 0} n^\nu \int _0^\infty d\sigma e^{-\epsilon \sigma }G^r_{\rho \nu }(z+ n\sigma )\,.\) 
